It is known in the prior art to use a swaging tap to push metal or other malleable material from the walls of an oversized hole toward the axis of the hole to reduce the effective diameter of the hole. Thus, the diameter of the resized hole has only narrow thread crests which are relatively weak at the smallest diameter. This was corrected by using a reamer to remove the metal at the crests of the threads to the correct diameter throughout the hole. That process left a hole which was still threaded but in which the crests of the threads had been removed to a uniform diameter. No metal was displaced from the thread crest to widen the crest more than the cutting action of the reamer did. In this invention the crest metal is not lost, but is displaced to add to the bearing surface of the re-sized hole.
The reaming method sacrificed some of the metal, thereby weakening the part. The use of a reamer can produce burrs and may not be as accurate in sizing the hole as the method of the present application.
Van Vleet U.S. Pat. Nos. 3,220,032 and 3,237,485 disclose the thread forms of a swaging tap which are most useful in the lead section of the tool disclosed herein because the use of those thread forms produces balanced axial forces at the two flanks of each turn of the thread and therefore do not tend to break the thread as readily as other thread geometries. Those patents relate only to the threading portion of the present tool, however. They do not disclose the remaining portions of the tool which are essential in forming a complete tool according to this invention.
Other patents known to applicant are Welles U.S. Pat. No. 3,067,509 and Hill U.S. Pat. No. 3,097,426. Each of these discloses a single tool for resizing a hole, and each shows a swaging tap section having tapered threads. The Hill patent also shows that the threads of section 18 are flattened to a constant outside diameter. However, that section is not the section that forms the final diameter of the hole. The final diameter is formed by reamer section 22. Each of these patents shows reamer sections for finishing the hole to its final size with the difficulties that such a process entails. None of these patents show the special surfaces found in the sections of the tool of the present invention which follow the swaging tap section. It is that combination of surfaces which gives the present tool its unique quality.